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New Models Uncover Path of Deadly Tsunami

February 7, 2005 –In medieval Japan, people believed that tsunamis came to shore when a giant sea serpent flapped its tail. The devastating waves would cease, said the myth, if a large bag of rice were placed on the serpent’s head.

Though modern-day predictions and solutions are quite a bit more sophisticated, they still remain incomplete, as two scientists detailed at a talk at the Marian Koshland Science Museum on Monday February 7. Civil engineers Philip Liu of Cornell University and Costas Synolakis of the University of Southern California presented preliminary models that recreate the devastating path of the December 26 Indian Ocean tsunami.

Based on mathematical models informed by field data from the recent tsunami and past tsunamis, Synolakis, part of a research group that traveled to the Maldive Islands in early January, and Liu, a member of a Sri Lanka research team, illustrated several interesting tsunami characteristics. Models have shown, for example, how the large wave “wrapped around” islands that were struck, so that the lee side of the islands actually suffered greater impact and therefore more damage. Interestingly, because of Sri Lanka’s proximity to India, the wrap around was incomplete and Colombo, Sri Lanka's capital, which faces India, was spared. But in the area between Sri Lanka and the Maldive Islands, which are lined with steep cliffs, waves actually bounced back and forth between the two land masses, causing additional destruction hours after the initial impact.

Liu and Synolakis described their fieldwork, which sometimes involved trekking through dangerous political and physical terrain. They gauged water level by examining water marks on buildings and debris caught in trees. And they took sediment samples that geologists will later compare to sediment left behind by past tsunamis; these comparisons could help to estimate the intensity of tsunamis that struck decades ago.

Though the magnitude of the recent tsunami was exceptional, tsunamis are not particularly rare and are under-reported by the media, said the researchers. Indeed, as Synolakis explained to an audience of policymakers, journalists, and members of the general public, the last 12 years of tsunami research and observations have drastically changed scientists’ views. Data on the timing and sequence of wave events from a 1992 Nicaraguan tsunami suggested that shoreline topography must be taken into account, hence drastically changing scientists’ models. Eyewitness accounts of a 1995 tsunami in the Mexican town of La Manzanilla, for example, proved for the first time that a tsunami’s “leading depression wave” causes the water to recede significantly before the actual wave hits. La Manzanilla’s bay actually emptied before a surge advanced up the shore several minutes later.

Both researchers endorsed installing additional tsunami early warning devices to complement the National Oceanic and Atmospheric Administration’s DART (deep ocean assessment and reporting of tsunamis) system, which employs buoys to transmit messages to satellites originating from ocean floor pressure sensors called tsunameters. Any future system deployed in the Indian Ocean must detect tsunamis reliably, said Synolakis, otherwise it will lose credibility among persons in the affected areas. The engineers also hope to improve inundation maps in order to create better evacuation maps for local populations.

But that populace must be educated, both scientists emphasized. “A tsunami warning system is useful but without education, people don’t know how to respond,” said Liu. Many affected by the recent tsunami did not know the warning signs, and perished as a result. “Education, education, education,” said Synolakis.